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1.1 Background
The drying process is a complex process of heat and mass transfer resulting in a direct transfer of humidity from some substance into hot air. The heat transfer, necessary for that process, can be direct, convective from the drying agent which flows around the drying material, or indirect, by different procedure (Salemović et al., 2014). Drying process has long been used from the time of old to dry food. For example, foods like meat, fish and so on were dried using sun as the drying medium to preserve them and prevent growth of micro –organisms (Dagbe et al., 2014). Majorly, substances are/were dried for the following reasons:
1. To remove moisture content which may otherwise lead to corrosion. One example is drying of gaseous fuels or benzene prior to chlorination.
2. To reduce the cost of transportation.
3. To make material more suitable for handling, as for soap powders, dye stuffs and fertilizers.
4. To provide definite properties, such as for example maintaining free flowing of salt.
5. To mitigate the activities of the micro-organisms that can cause spoilage and decay in food products if moisture were present in the food.
Modeling of drying processes and kinetics is a tool for process control and necessary to choose suitable method of drying for a specific product. Developed models fall into three categories namely the theoretical, semi-theoretical and empirical. Semi-theoretical models offer a compromise between theory and ease of application (Khazaei and Daneshmandi, 2007). Semi-theoretical models are Lewis, Page, Henderson and Pabis, logarithmic, two terms and two terms exponential, models are used widely for designing as well as selection of optimum drying conditions and for accurate prediction of simultaneous heat and mass transfer phenomena during drying process. It also leads to the production of high quality product and increase in the energy efficiency of drying system. Thin-layer drying models have been used to describe the drying process of several agricultural products.
In the Chemical Engineering Laboratory of Afe Babalola University the PID controller of our tray drier system has been giving unsatisfactory performances. It is envisaged to replace the controller in future with an advanced one-model predictive controller. In order to carry out this efficiently a low dimensional lumped parameter is sought. Some model in literature are too complex (PDE’s) to be used for control purposes or do not match the mechanics of the tray drier of interest. However, the greatest drawback of the tray dryer is uneven drying because of poor airflow distribution in the drying chamber that can be removed by implementing some modification in the dryer design. (Katiyar et al., 2013). Thin layer drying kinetics is needed for design, operation and optimization of food crops dryers (Olawale et al., 2012). Therefore this project is aimed at developing lumped parameter model that will be suitable for control, since most of the models developed are too emperical, strongly non linear, and too complex to characterize tuning parameters in a control system.
1.2 Statement of Problem
The PID controller in our laboratory tray dryer has been giving unsatisfactory performances. It is envisaged to replace the controller in future with a more advanced one – model predictive controller. To be able to do this easily and efficiently, a low dimensional lumped parametermodel is sought. Some available in literature are either too complex (PDEs) to be used for control purposes or do not match the mechanics of the tray dryer of interest.
1.3 Scope of Study
The scope of study covers the modelling and simulation of a convective drying process of a thin slice layers of potato, using a tray dryer as the drying medium and MATLAB software will be employed as the simulation tool for this project.
1.4 Aim of Study
The aim of this work is to derive a mathematical model suitable for control. Potato will be dried in a tray dryer in order to define the essential drying parameters of a static thin layer of potato and plantain of known magnitude of thickness which could be used subsequently for control of these agricultural products and similar natural products in a ‘Tray dryer’.
1.5 Objectives
The following objectives are expected to be carried out:
i) Study and analyze existing mathematical models developed for tray dryer system drying some agricultural products
ii) Develop a mathematical model for a tray dryer using potato as the sample in the tray dryer.
iii) Simulation of the models using MATLAB software
iv) Compare the result with experimental data.

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